The present invention relates to ski bindings in general, especially to bindings for cross country skis, and more particularly to improvements in sole plates of ski bindings. Still more particularly, the invention relates to improvements in the construction of sole plates, in the manner of mounting the sole plates on skis, and in the manner of securing the sole plates to the toe portions of boots.
German Pat. No. 1,578,912 discloses a ski binding wherein the front part of the sole plate is pivotably coupled to the ski and comprises a frame having two longitudinally extending parallel rods which are connected to each other by a transversely extending stiffening member. The stiffening member has two eyelets whose axes are parallel to the skiing direction and through which the rods extend, and serves as a rest for the sole of a boot as well as to enhance the rigidity of the sole plate. Such rigidity is not guaranteed under all circumstances, mainly because the rods simply pass through the eyelets of the stiffening member and are likely to move lengthwise relative to each other and/or the stiffening member, especially if the sole plate is subjected to pronounced twisting stresses, e.g., if the heel of the boot tends to move laterally of the ski.
The sole plate which is disclosed in the German patent further carries a conventional connecting device which engages the foremost portion of the sole of a ski boot in front of the toe. The connecting device is designed to properly engage and hold a sole of average thickness. Furthermore, the just discussed connecting device extends forwardly beyond the pivot means for the sole plate; this limits the angle through which the sole plate can pivot with respect to the ski.
A ski binding, especially a binding for use on cross country skis, should be capable of engaging different types of boots, i.e., not only ski boots but also other types of boots (for example, boots which are designed for mountain climbing). The aforediscussed patented binding is incapable of properly engaging different types of boots, especially when the thickness of the sole deviates considerably from an average thickness. Also, it is desirable to employ a relatively simple but reliable connecting device (e.g., a simple pivotably mounted yoke) which can be moved into satisfactory engagement with the tip of the sole in front of and below the toe portion of the boot. If such a simple yoke engages the tip of a relatively thin sole, the boot is located closer to the front end of the ski than if the yoke engages the tip of a relatively thick sole. This will be readily understood by considering that the yoke is pivotable about a horizontal axis which is normal to the longitudinal direction of the ski. The shape of the toe portion of a boot also affects the angular position of the yoke. In other words, the position of a boot with respect to the pivot axis for the sole plate of the binding depends on the thickness of the sole, and to a certain extent, on certain other factors (including the aforementioned configuration of the toe portion). It can happen that (especially if the sole is very thin) the foremost part of the sole extends forwardly beyond the pivot axis of the sole plate. This interferes with movements of the skier's legs, especially in cross country running. On the other hand, if the tip of the sole is located too far away from the pivot for the sole plate (i.e., if the sole is very thick), the skier must lift the corresponding portion of the ski (and hence his or her weight) through a distance which approximates or equals the distance between the tip of the boot and the pivot axis for the sole plate (such pivot axis should not be confused with the pivot axis for the aforementioned yoke which engages the tip of the sole in front of the toe portion of the boot). It has been found that the boot is located in an optimum position if its tip is closely adjacent the pivot for the sole plate. This is not possible with the binding which is disclosed in the aforementioned German patent, partly due to the (self-releasing) nature and partly due to design of the connecting device which engages the tip of the sole.